When it is desired to move an article or piece of machinery from one location to another, it is well known to connect the item to be moved to a continuous looped chain formed of rigid links which engages with the sprocket teeth of a rotating drive sprocket wheel. Such a drive chain will only be useful in situations where the item to be moved follows a looped path within a single plane. Furthermore, articles integrally connected to the drive chain may not be removed from the drive apparatus.
Articles which must move along a path with multiple curvatures and changes in elevation may be conveniently handled by a bi-planar tow chain. This chain is formed of multiple rigid lengths which are joined to permit rotation about two axes. A tilt-tray assembly or other carriage may be fixed to the tow chain together with a number of guide wheels which stabilize the carriage in a fixed track.
In a conventional caterpillar drive assembly the sprocket and chain apparatus engages with the tow chain to advance the chain along a predetermined path. A number of drive chain and spocket wheel assemblies may be placed along the tow chain path where the path is substantially linear to drive the tow chain around curves and to different elevations.
One known method of engaging the drive chain with the tow chain employs downwardly depending nylon dogs spaced along the tow chain and U-shaped aluminum dogs affixed at intervals to the drive chain which engage the tow chain dogs and advance the tow chain. This type of apparatus results in sharp shocks to the tow chain each time a depending dog is grasped by the drive chain. Repeated shocks result in a jerky motion of the tow chain and rapid wear to the mechanical elements of the system which must sustain repeated severe shocks. These shocks and the wear to the system is particularly pronounced at high speeds such as would be desirable in a tilt-tray sortation system.
What is needed is a chain drive which smoothly engages with a tow chain to effectively transmit drive power and which may operate at high speeds to provide even motion of the driven chain with a minimum of wear to the system parts.